Fabaceous and Cucurbitaceous Hosts Are Infected With Distinct Populations of the Powdery Mildew Species Podosphaera xanthii

Two species of powdery mildew, Podosphaera xanthii and Erysiphe vignae , cause disease in mungbean ( Vigna radiata ) in Australia. P. xanthii is reported to have a wide host range, occurring worldwide on many different host families, including the Cucurbitaceae. It is unclear whether the P. xanthii populations that infect mungbean also infect other crops, such as cucurbits. In this study, we conducted cross‐inoculation experiments to determine whether P. xanthii collected from mungbean infects a range of cucurbits; and conversely, whether P. xanthii from cucurbits infect mungbean and other Vigna species. P. xanthii collected from mungbean heavily infected black gram ( Vigna mungo ), native mungbean ( V. radiata subsp. sublobata ) and maloga bean ( Vigna lanceolata ); it did not infect zucchini ( Cucurbita pepo ), butternut pumpkin ( Cucurbita moschata ), cucumber ( Cucumis sativus ) or watermelon ( Citrullus lanatus ); and it produced small colonies on squash ( C. pepo ), marrow ( C. pepo ) and pumpkin ( Cucurbita maxima ). Conversely, P. xanthii from melon ( Cucumis melo ) heavily infected zucchini, pumpkin, butternut pumpkin and cucumber; it did not infect mungbean or black gram; it caused moderate infections on native mungbean and maloga bean. A search for genetic markers that differentiate the P. xanthii populations collected from mungbean and melon, used as inoculum sources in this investigation, revealed a 377 bp difference in the size of the promoter region of the cyp51 gene. This was found to be a robust molecular marker in this work. This study revealed clear differences in the host range of the two P. xanthii populations infecting fabaceous and cucurbitaceous species.